1. Field Of The Invention
The present invention relates generally to remote control of downhole tools, and more particularly but not by way of limitation to signaling techniques for communicating with a downhole tool.
2. Description Of The Prior Art
Traditionally, downhole tools such as those utilized in drill stem testing of oil and gas wells have been controlled either by physical manipulation of the pipe string which carries the tools or by changing the pressure applied to a column of fluid standing in the well, with that pressure being directly mechanically applied to a power piston of the tool so as to move an operating element of the tool. This second mode of operation includes those tools which are directly operated by changing well annulus pressure which is communicated with a power piston of the tools, or so-called annulus pressure responsive tools.
More recently, the development of downhole tools including programmed electronic controllers has made possible the use of remote controlled tools which may receive command signals transmitted from a remote command station, located at the earth's surface, through any one of several means to a receiver contained in the tool. The programmed electronic controller then causes the operating element of the tool to be actuated through any one of several types of operating systems in response to the remotely received command signal.
The communication systems typically provided for remote control tools in the prior art have utilized distinctly different command signals to instruct the tool to carry out each desired operation. Thus, a tool that has two positions such as an open position and a closed position of a valve will utilize two distinct command signals, one to tell the tool to move to an open position and another to tell the tool to move to a closed position. The system is further complicated when a tool has more than two positions and thus a multitude of distinct command signals are required to communicate with the tool.